Interface instability in the drawing process of copper/tantalum conductors

Copper/tantalum test billets have been cold drawn, using the process developed for the elaboration of copper/niobium multifilamentary conductors, for the development of high strength and high conductivity conductors for high pulsed magnetic fields. After a section reduction of 60%, a macroscopic roughness of the tantalum surface has been observed: two sets of perpendicular undulations developed (pa;allel and perpendicular to the drawing axis), with wavelengths in the 100 mu m range. This phenomenon, observed for the first time on bulk materials, is interpreted in terms of the Grinfeld instability: the associated wavelength, calculated in the case of a shear stress discontinuity at the interface between b.c.c. tantalum and f.c.c. copper, is found in the right magnitude range. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.